1. The Field of the Invention
The present invention relates to methods for manufacturing semiconductor devices. More particularly, the present invention relates to methods for fabricating a semiconductor device, such as a capacitor, which utilize in situ passivation of dielectric thin films during fabrication.
2. The Relevant Technology
As integrated circuit technology has progressed, it has become possible to store ever-increasing amounts of digital data in a smaller space at less expense and still access the data randomly, quickly and reliably. Central to this increased ability to store and retrieve data has been the dynamic random access memory (DRAM), fabricated as an integrated circuit. The memory cells of DRAMs are comprised of two main components, a transistor and a capacitor. The capacitor of each memory cell functions to store an electrical charge representing a digital value (e.g., a charged capacitor representing a 1 and a discharged capacitor representing a 0) with the transistor acting as a switch to connect the capacitor to the "outside world" via decoding and other circuitry. In order to function properly, the capacitor must possess a minimum amount of capacitance. If a capacitor exhibits too little capacitance, it will cause errors in data storage.
The capacitive value of a capacitor is dependent upon the dielectric constant of the material placed between the plates of the capacitor, the distance between the plates, and the effective area of the plates. In the case of integrated circuits, the material used as a dielectric between the plates is generally limited to only a few materials.
The interaction of dielectric materials and capacitor electrode materials plays a critical role in determining electrical properties such as leakage current of capacitors in integrated circuits and advanced packages. The electrode material can interact with the dielectric material during deposition and further processing. For example, the electrode material can adsorb some of the oxygen from the dielectric film, making the dielectric film oxygen deficient. The oxygen deficient dielectric film demonstrates current leakage , and is unacceptable for use in a DRAM or other semiconductor applications.
Various approaches have been developed in an attempt to reduce leakage current problems in capacitors. For example, U.S. Pat. No. 5,641,702 to Imai et al. discloses a method of forming an integrated circuit capacitor with an insulating film having a high permittivity, which includes annealing the insulating film in a reactive oxygen atmosphere to reduce leakage current in the capacitor. In U.S. Pat. No. 5,189,503 to Suguro et al., a capacitor having a two-part dielectric insulating layer is disclosed, including a first metal oxide film with pieces of a dissimilar metal element added to the oxide, such as tantalum oxide with a zirconium additive, and a second metal oxide film such as tungsten oxide. The disclosure in the Suguro patent indicates that excessive oxygen may be added to a tantalum oxide layer to reduce oxygen deficiency and the associated leakage current. In U.S. Pat. No. 5,153,685 to Murata et al., an integrated circuit capacitor having a two-part dielectric layer including silicon nitride and silicon dioxide is disclosed. The silicon nitride is formed on the lower electrode, and the silicon dioxide is formed from the silicon nitride by a high pressure oxidation process.
While the above approaches have made some progress in reducing leakage current problems in capacitors, there is still a need for improved capacitor fabrication methods that further reduce or prevent the adsorption of oxygen from dielectric films by capacitor electrodes.